<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .father {
        display: flex;
        align-items: center;
        justify-content: center;
        width: 300px;
        height: 300px;
        background-color: pink;
    }
</style>
<body>
    
    
    <div class="father">
        <span class=“son”>我是子元素</span>
    </div>
</body>
</html>